Hydrocarbon synthesis operation



Patented Aug. 16, 1949 UNITED STATES PATENT OFFICE rrYnnooAnnoNSYNTHESIS OPERATION Alexis Voorhies, Jr., Baton Rouge, La., assignor toStandard Oil Development Company, a corporation of Delaware No Drawing.Application April 27, 1948, Serial No. 23,629

6 Claims. (01. zoo-449.6)

so that excessive carbonization with attendant fragmentation of thecatalyst in the reaction zone does not occur. In accordance with theinvention unpromoted or underpromoted' iron group catalysts are promotedin situ in'a catalytic reaction zone during the initial hours of asynthesis operation until the optimum concentration of promoter isreached. Then as necessary and in order to maintain high yields,additional promoter may be added during the hydrocarbon synthesis run.Simultaneously, carbon formation is controlled in the hydrocarbonsynthesis zone by the addition of water.

It is well known in the art to conduct hydrocarbon synthesis reactionsby contacting hydrogen and oxides of carbon with catalysts under varioustemperature and pressure conditions. The catalyst employed is usuallyselected from the iron group metals, as for example, iron, cobait andnickel. The catalysts are utilized either alone or are employed inconjunction with carriers, such as kieselguhr, diatomace'ous earth,synthetic gels, silica, and alumina. Promoters, such as oxides or saltsof sodium, potassium, chromium, zinc, aluminum, magnesium, and the rareearth metals are used with the iron group metals. These catalysts areemployed in either fixed bed or fluid catalystoperations.

The temperatures employed in the synthesis reaction vary widely, as forexample, in the range from about 300 F. to about 800 F. and are generally in the range from about 350 'F. to about 750 F. The pressures,likewise, vary considerably and are a function of other operatingconmonoxide to about 2 mols of hydrogen, while 55' 2 when an ironcatalyst is utilized the fresh feed composition is not so critical andordinarily lies between 0.8 mol and 2.5 mols of hydrogen per mol ofcarbon monoxide.

The synthesis gases comprising hydrogen and carbon monoxide are producedby various procedures. Methane or natural gas may be oxidized with areducible metal oxide, with pure oxygen or with gases comprising oxygen.Coal, shale and solid other hydrocarbons may be reacted with steamand/or carbon dioxide to form hydrogen and carbon monoxide for use as asynthesis gas. The reaction may be conducted in a single or in aplurality of stages. For example, one procedure is to reform methane ornatural gas using steam and carbon dioxide for the production of carbonmonoxide and hydrogen.

reactions are generally conducted at tempera-- tures in the range fromabout 1400 F. to about 2000" I".v When the synthesis gases are produced,

by utilizing oxygen and methane or natural gas,

a the temperatures in the reaction zone are usually in the range 3000 F.

It is also known in the art to contact gases and solids by passing thegases upwardly through an enlarged treating zone, containing a body offinely divided solids to be contacted, at a controlled velocity tomaintain the solids in the treating zone in a quasi-liquid like state.Under properly controlled conditions, the subdivided solid particles arenot only maintained in a highly turbulent. quash-liquid and ebullientstate, but there exists a'rapid and overall circulation of the fluidizedsolids throughout the fluid bed. In these fluid operations the catalystparticles generally comprise particles having particle sizes in therange from about 0 to 200 microns and. higher- These particles aremaintained in a fluid ebullient state by means of an upflowingsuspending gas, the velocity of which is in the range of about 0.1 to 5feet per second and higher.

The invention finds specific application in a hydrocarbon synthesisreaction wherein the synthesis gases are reacted in the presence of asuitable catalyst to form hydrocarbon constituents containing more, thanone carbon-atom in the molecule. For example, in this process one of theimportant problems confronting the development of the synthesis processis that carbon builds up on the catalyst causing fragmentation and lossof the catalyst from the reactor by elutriation. Although, a certainamount 01. car-' from about 2000 F. to about r 3 bon may be desirable onthe catalyst surface. this factor must be controlled.

In accordance with the invention extraneous water vapor is added to thefeed gas and at the same time a}: unpromoted or under-promoted catalystis utilized during the initial stages of the synthesis. This unpromotedor under-promoted catalyst which preferably comprises an iron catalystis then promoted in situ' ina :fluid catalyst reactor during the initialstages of the synthesis operation until the optimum concentrat-ion ofpromoter is reached. As necessary to maintain high yields, additionalpromoter may be added during the run.

Experience in hydrocarbon synthesis has shown that the function of thepromoter on the catalyst is primarily to increase selectivity andactivity of the catalyst. 'However, an excess amount of promoter willresult in excessive carbonization of the catalyst with resultingcatalyst disintegration. As discussed herebefore the promoters commonlyused are alkali compounds, such as the salts or hydroxides of potassium,sodium and lithium. A specifically effective promoter from thestandpoint of activity and selectivity is potassium fluoride. However ithas been demonstrated that excessive amounts of this particular promoterwill result in excessive catalyst carbonization.

The eil'ects of a promoter and the need therefor depend critically onthe conditions of hydro-carbon synthesis. For example, those conditionsmost likely to give good product quality, particularly high temperatureoperation in the range from about 600 F. to 750 F., unfortunately demandthe use of greater amounts of promoter thando the milder conditions.This entails a greater risk from the standpoint of catalystcarbonization. There has recently been discovered one efiective means ofrepressing catalyst carbonization and resulting disintegration, and thatis by the introduction of extraneous water at the reactor inlet. Thisexpedient, however, has a tendency to decrease the selectivity of thecatalyst when the amount of water exceeds a certain critical value,which in turn depends upon the catalyst'composition and the conditionsof operation.

This invention embraces a novel and satisfactory method for takingoptimum advantage of the favorable characteristics of the catalystpromoter and the use of water additions. As just pointed out, the eifectof catalyst promoter and water addition are in many ways just thereverse increased amounts of promoter tend to give greater activity andselectivity but more carbonization, just the opposite of the result ofincreased water addition.

According to the present invention, the hydrocarbon synthesis processmay be conducted a follows:

An unpromoted catalyst, specifically a, rather pure iron oxide such assintered pyrites ash, is charged to the reactor in the regular way. Thisprocess has reference to a fluid catalyst operation. Catalyst chargedwould be of conventional particle size. duced in the conventionalfashion.

Synthesis is begun at predetermined standard conditions, which wouldgive good selectivity, good activity, and good product quality if thecatalyst temperatures in the range from about 550 F. to-

750 F.; mol ratios of hydrogen to carbon mon- The unpromoted iron oxideis res.

of about 10 to 200 SCI" of feed gas per lb. of cataalyst in the reactorper hour are employed. Such conditions, as stated. would initially givepoor selectivity and poor activity with an unpromoted or under-promotedcatalyst; but on the other hand, rather complete freedom from carbonformation difllculties, i.-e. deposition of carbonaceous material on thecatalyst, is secured.

From the start of the synthesis run, a small amount of promoter is addedto the reactor. The purpose is to obtain a slow and even impregnation ofthe catalyst with the promoter, and to furnish a means of determiningjust when the optimum amount of promoter has been added. For example,the selectivity is closely watched while it increases to a satisfactoryvalue, such as 190-200 cc. of hydrocarbons containing four carbon atomsin the molecule and higher boiling constituents per cubic meter ofHa-i-CO con-f to suppress catalyst carbonization. The invention,however, is not limited to the introduction of catalyst by means of anaqueous solution. Other methods of introducing the promoter may beemployed. For example, the promoter may be introduced as a dry powderinto the total feed gas stream or through a side stream employingrecycle or fresh feed gases as a carrying medium. Still another methodis to employ a solution of the promoter in hydrocarbon synthesis productwater, which normally contains organic acids and other compounds whichwould promote the solubility of certain promoter compounds.

The promoter addition would be stopped, as mentioned above, when theselectivity has reached a-predetermined value, and before the promoteris sufficiently great to begin to cause excessive catalystcarbonization. For example, a-O.l% solution of KF is injected over aperiod of about 150 hours at such a rate as to result in a 1%concentivities begin todecrease while water addition is normal, theremedy is to begin to inject more promoter-until the selectivity hasregained its original value. Contrariwise, if carbon formation begins toincrease some time during the run, the rate of water addition isincreased to just such a point as to correct this situation.

In any particular situation, it is obvious that the success of theobservation will depend on the experience and goodjudgment of theoperatorin applying the teachings of this invention for it is impossibleto disclose the precise amount of water and/or promoter that must beemployed so as to cover every conceivable contingency. Rather thepresent invention functions as a guide and sign post indicating to theoperator the manner of achieving maximum efficiency during a hydrocarbonsynthesis operation. Experience Mn 7 ing a very large number oflaboratory and pilot Broad Preferred Mol ratio of H, to H10 in totalfeed 5-25 7-15 Wgt. Percent of Promoter (based iron and calculated asKF) 0.1-5 0.5-2.5

This type of operation is especially applicable to the use of a cheapcatalyst base, such as sintered pyrites ash whichmay be continuouslyreplaced by daily or more frequentadditions and removal of catalyst fromthe reactor. The added material would preferably be the unpromoted ironoxide, either with or without prior reduction. However, the invention isnot to be limited to the use of sintered pyrites ash, but will apply aswell as any catalyst base whether unpromoted or partially promoted.

The process of the invention is not to be limited by any theory as tomode of operation but only in and by the following claims in which it isdesired to claim all novelty insofar as the prior art permits.

I claim:

1. An improved hydrocarbon synthesis process which comprises reactingtogether, under synthesis conditions, hydrogen and carbon monoxideinitially in the presence of an unpromoted powdered iron catalyst in theform of a fluidized bed contained in a reaction zone, adding an alkalimetal compound to the reaction zone at a slow rate during such a periodof time as to cause a slow and homogeneous impregnation of said alkalimetal compound within said catalyst, and to the extent that the desiredyields of normally liquid hydrocarbons are obtained from the reactionzone, whereupon the feeding of the alkali metal compound isdiscontinued, the amount of said promoter with respect to the catalystand contained thereon lying within the limits of from about 0.1 to 5 wt.after the initial period, and adding water to the reaction zone torepress carbon formation in an amount such that the feed to the reactionzone contains 5 to 25 mols of hydrogen per mol of water.

6 2. The method of claim 1 in which the amount of alkali metal compoundmaintained in the cat alyst is from about 0.5-2.5 weight percent basedon the iron and the amount of water fed to the reaction zone is suchthat 7-15 mols of hydrogen per mol of water are contained in the totalfeed.

3. The method of claim 2 in which the alkali metal compound is KF.

4. The method of claim 3 in which the iron catalyst is a sinteredpyrites ash.

5. Improved hydrocarbon synthesis reaction which comprises introducingfeed gases comprising carbon monoxide and hydrogen into a hydrocarbonsynthesis reaction zone, introducing water into said reaction zone, inamounts of from about 1 mol per 7-15 mols of hydrogen inthe total feed,contacting the feed gases with a catalyst selected from the groupconsisting of iron, cobalt and nickel in said reaction zone undertemperature and pressure conditions adapted to produce the desiredsynthesis, said catalyst being characterized by containing no promoterduring the initial stages of the reaction, gradually adding a promoterto the reaction zone until the selectivity of the catalyst is increasedto produce a product of 180 to 210 cc. of hydrocarbons having 4 carbonatoms in the molecule and higher boiling constituents per cubic meter ofhydrogen and carbon monoxide consumed and thereafter'adding additionalpromoter to maintain the catalyst activity in this range.

6. The method of claim 5 further characterized in that the promoter isKF and that the same is added in the form of a dilute aqueous solutionduring a period of about 150 hours and until the iron catalyst ishomoeneously impregnated with about 1% by weight of said promoter.

- f ALEIHS VOORHIES, JR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,183,145 Michael et al. Dec.'12, 1939 2,254,806 Michael Sept. 2, 1941 2,395,875 Kearby Mar. 5, 19462,447,505 Johnson Aug. 24, 1948

